1. Field of the Invention
This invention relates to a magnetically operated latch.
2. Description of the Prior Art
U.S. Pat. No. 3,600,019 discloses a latch mechanism which is for slidable sashes and which can be locked in the latched position. The mechanism comprises a latching member which is mounted to be manually turned in a vertical plane for engagement with a keeper, a catch which is mounted to reciprocate in a path transverse to the plane and spring-biased to interengage with the latching member when the latter is engaged with the keeper, a catch release member which is mounted to reciprocate in a vertical path, and a bell-crank lever operative to retract the catch from the latching member against the action of the spring in response to upward movement of the catch release member. The latter is detained against upward movement by a first permanent magnet protruding into a bore therein from a bore in a block mounting the latching member. A second permanent magnet fixed in the inner end of the latter bore repels the first magnet into that detaining position. An actuator manually reciprocable in a vertical path can be raised to a position in which a third permanent magnet fixed thereto repels the first magnet into the bore the block against the action of the second magnet and so allows the catch release member to be raised by that same actuator to retract the catch. Subsequent lowering of the actuator allows the second magnet to repel the first magnet to against an external surface of the release member. When the latching member is returned into its latched position, the action of the spring on the bell-crank lever re-engages the catch and lowers the catch release member to enable the second magnet to repel the first magnet back into its detaining position. This mechanism is very complicated and employs three magnets, and is thus very costly.
U.S. Pat. No. 3,744,833 discloses a latch comprised of first and second permanent magnets mounted in mutually repelling relation upon a box so that the first is urged into an engaging position in which it engages in a recess in a cover of the box, and a third permanent magnet which when brought up to an outside wall of the box at a location close the first magnet, which is vertically displaceable in an open-topped cavity in the wall, overcomes the repulsion and withdraws the first magnet. Upon removal of the third magnet, the repulsion between the first magnet and the second magnet, which is fixed to the inside of the box, returns the first magnet to its engaging position. This latch uses three magnets, which are costly.